SNP Marker of Breast and Ovarian Cancer Risk
The invention provides methods for predicting an increased risk or probability of developing breast or ovarian cancer in a patient based upon the patient's KRAS-Variant and BRCA status.
This application is related to provisional application U.S. Ser. No. 61/150,645, filed Feb. 6, 2009, and U.S. Ser. No. 61/267,284, filed Dec. 7, 2009, the contents which are each herein incorporated by reference in their entirety.
FIELD OF THE INVENTIONThis invention relates generally to the fields of cancer and molecular biology. The invention provides methods for predicting increased risk of developing breast and ovarian cancer, including hereditary breast ovarian syndrome.
BACKGROUND OF THE INVENTIONThe genetics of Breast/Ovarian Cancer Syndrome is autosomal dominant with reduced penetrance. In simple terms, this means that the syndrome runs through families: (1) both sexes can be carriers (mostly women get the disease but men can both pass it on and occasionally get breast cancer); (2) most generations will likely have breast cancer; (3) occasionally women carriers either die young before they have the time to manifest disease (and yet have offspring who get it) or they never develop breast or ovarian cancer and die of old age (the latter people are said to have “reduced penetrance” because they never develop cancer). Pedigree analysis and genetic counseling is absolutely essential to the proper workup of a family prior to any lab work.
In 1994, the first gene associated with breast cancer, BRCA1 (BReast CAncer1) was identified on chromosome 17. A year later, a second gene associated with breast cancer, BRCA2, was discovered on chromosome 13. When individuals carry a mutated form of either BRCA1 or BRCA2, they have an increased risk of developing breast or ovarian cancer at some point in their lives. Not all hereditary breast and ovarian cancers are caused by BRCA1 and BRCA2.
Accordingly, there is a need for the identification of genetic markers that indicate a predisposition for developing cancer, e.g., ovarian cancer and/or breast cancer, that can be used to identify subjects that have an increased susceptibility for developing cancer, i.e., they are predisposed to develop cancer. Even though there has been progress in the field of cancer detection, there still remains a need in the art for the identification of new genetic markers for a variety of cancers that can be easily used in clinical applications.
SUMMARY OF THE INVENTIONThe invention provides a genetic test for predicting the risk of an individual developing breast cancer, ovarian cancer, and hereditary breast/ovarian syndrome. The current test for these conditions is BRCA, a time-consuming test which is predictive of hereditary breast and ovarian cancer risk in about 5 percent of individuals, most of whom are of Ashkenazi Jewish descent. Methods of the invention provide a simpler test, which determines the presence or absence of the LCS6-SNP (also known as the KRAS-Variant). Studies show that the KRAS-Variant is found in up to 27% of sporadic ovarian cancer. Critically, the KRAS-Variant is present in 61% of BRCA-negative ovarian cancer patients. Thus, the invention represents a breakthrough method of diagnosing and prognosing patients from whom, until now, a genetic test predictive of cancer risk was unavailable. Moreover, the presence of the KRAS-Variant modifies the effect on BRCA1. The presence of both the KRAS-Variant and a BRCA1 mutation results in an increased the risk of that patient developing both breast and ovarian cancers. Also critically, the presence of the KRAS-Variant in ovarian cancer is a biomarker and predictor of poor prognosis because the presence of the KRAS-Variant is associated with more advanced stages of the disease, non-responsive forms of the disease, and decreased patient survival.
Specifically, the invention provides a method of predicting an increased risk of hereditary breast/ovarian cancer syndrome (HBOC syndrome or HBOS) in a subject, including detecting a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of the SNP indicates an increased risk of HBOC syndrome in the subject. In one aspect of this method, the subject is BRCA1 or BRCA2 negative. Alternatively, in certain aspects of this method, the subject is BRCA1 or BRCA2 positive. Furthermore, in certain embodiments of this method, the subject is of non-Jewish or non-Ashkenazi Jewish descent.
The invention further provides a method of predicting an increased risk of developing ovarian cancer or breast cancer in a subject, including detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of the BRCA1 mutation and the SNP indicates an increased risk of developing breast or ovarian cancer. In one embodiment of this method, the subject has hereditary breast/ovarian syndrome (HBOS, or HBOC syndrome). In another embodiment, the subject is BRCA2 negative. Alternatively, or in addition, the subject is of non-Jewish or non-Ashkenazi Jewish descent. In certain embodiments, BRCA1 mutations of this method are non-founder mutations.
The invention also provides a method of predicting an increased risk of developing both breast and ovarian cancer in a subject having HBOS (or HBOC syndrome) including detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of the BRCA1 mutation and the SNP indicates an increased risk of developing both breast and ovarian cancer. In certain aspects of this method the subject is of non-Jewish or non-Ashkenazi Jewish descent. In other aspects of this method, BRCA1 mutations of this method are non-founder mutations.
The invention is based upon the unexpected discovery that the presence of a SNP in the 3′ untranslated region (UTR) of KRAS, referred to herein as the “LCS6 SNP,” or the “KRAS-Variant”is predictive of Hereditary Breast/Ovarian Syndrome (HBOS, also known as Hereditary Breast/Ovarian Cancer (HBOC) syndrome).
Hereditary breast ovarian cancer (HBOC) syndrome is a syndrome that causes female carriers to be at increased risk for both breast and ovarian cancer. Risk factors for this syndrome include: an early age of onset of breast cancer (often before age 50);
family history of breast and/or ovarian cancer; increased chance of bilateral cancers (cancer that develop in both breasts, or both ovaries, independently) or an individual with both breast and ovarian cancer; an autosomal dominant pattern of inheritance (vertical transmission through either the mother or father's side of the family). Other factors that increase the chance that a family has the hereditary breast ovarian cancer syndrome include: family history of male breast cancer or Ashkenazi Jewish ancestry.
In 1990, DNA linkage studies on large families with the above characteristics identified the first gene associated with breast cancer. Scientists named this gene “breast cancer 1” or BRCA1. BRCA1 is located on chromosome 17. Mutations in the gene are transmitted in an autosomal dominant pattern in a family. Since it was clear that not all breast cancer families were linked to BRCA1, studies continued and in 1994, scientists discovered another gene (similar to BRCA1), and named it BRCA2. BRCA2 is located on chromosome 13. Mutations in this gene are also transmitted in an autosomal dominant pattern in a family. Both BRCA1 and BRCA2 are tumor suppressor genes that usually have the job of controlling cell growth and cell death. Everyone has two BRCA1 (one on each chromosome #17) and two BRCA2 genes (one on each chromosome #13). When a person has one altered or mutated copy of either the BRCA1 or BRCA2 gene, their risk for various types of cancer increases (U.S. Pat. Nos. 6,051,379; 6,083,698; 6,492,109; and 7,250,497; the contents of which are each herein incorporated by reference in their entirety). However, at least one-third of breast cancers which seem to run in families are not linked to BRCA1 or BRCA2, suggesting the existence of an additional hereditary breast cancer gene or genes.
There are three human RAS genes comprising HRAS, KRAS, and NRAS. Each gene comprises multiple miRNA complementary sites in the 3′UTR of their mRNA transcripts. Specifically, each human RAS gene comprises multiple let-7 complementary sites (LCSs). The let-7 family-of-microRNAs (miRNAs) are global genetic regulators important in controlling lung cancer oncogene expression by binding to the 3′UTRs (untranslated regions) of their target messenger RNAs (mRNAs).
Specifically, the term “let-7 complementary site” is meant to describe any region of a gene or gene transcript that binds a member of the let-7 family of miRNAs. Moreover, this term encompasses those sequences within a gene or gene transcript that are complementary to the sequence of a let-7 family miRNA. The term “complementary” describes a threshold of binding between two sequences wherein a majority of nucleotides in each sequence are capable of binding to a majority of nucleotides within the other sequence in trans.
The Human KRAS 3′ UTR comprises 8 LCSs named LCS1-LCS8, respectively. For the following sequences, thymine (T) may be substituted for uracil (U). LCS1 comprises the sequence GACAGUGGAAGUUUUUUUUUCCUCG (SEQ ID NO: 1). LCS2 comprises the sequence AUUAGUGUCAUCUUGCCUC (SEQ ID NO: 2). LCS3 comprises the sequence AAUGCCCUACAUCUUAUUUUCCUCA (SEQ ID NO: 3). LCS4 comprises the sequence GGUUCAAGCGAUUCUCGUGCCUCG (SEQ ID NO: 4). LCS5 comprises the sequence GGCUGGUCCGAACUCCUGACCUCA (SEQ ID NO: 5). LCS6 comprises the sequence GAUUCACCCACCUUGGCCUCA (SEQ ID NO: 6). LCS7 comprises the sequence GGGUGUUAAGACUUGACACAGUACCUCG (SEQ ID NO: 7). LCS8 comprises the sequence AGUGCUUAUGAGGGGAUAUUUAGGCCUC (SEQ ID NO: 8).
Human KRAS has two wild type forms, encoded by transcripts a and b, which provided below as SEQ ID NOs: 9 and 10, respectively. The sequences of each human KRAS transcript, containing the LCS6 SNP (KRAS-Variant), are provided below as SEQ ID NOs: 11 and 12.
Human KRAS, transcript variant a, is encoded by the following mRNA sequence (NCBI Accession No. NM—033360 and SEQ ID NO: 9) (untranslated regions are bolded, LCS6 is underlined):
Human KRAS, transcript variant b, is encoded by the following mRNA sequence (NCBI Accession No. NM—004985 and SEQ ID NO: 10) (untranslated regions are bolded, LCS6 is underlined):
Human KRAS, transcript variant a, comprising the LCS6 SNP (KRAS-Variant), is encoded by the following mRNA sequence (SEQ ID NO: 11) (untranslated regions are bolded, LCS6 is underlined, SNP is capitalized):
Human KRAS, transcript variant b, comprising the LCS6 SNP (KRAS-Variant), is encoded by the following mRNA sequence (SEQ ID NO: 12) (untranslated regions are bolded, LCS6 is underlined, SNP is capitalized):
The present invention encompasses a SNP within the 3′UTR of KRAS. Specifically, this SNP is the result of a substitution of a G for a U at position 4 of SEQ ID NO: 6 of LCS6. This LCS6 SNP (KRAS-Variant) comprises the sequence GAUGCACCCACCUUGGCCUCA (SNP bolded for emphasis) (SEQ ID NO: 13).
The KRAS-Variant leads to altered KRAS expression by disrupting the miRNA regulation of a KRAS. The identification and characterization of the KRAS-Variant is further described in International Application No. PCT/US08/65302 (WO 2008/151004), the contents of which are incorporated by reference in its entirety.
It was determined that the presence of the KRAS-Variant is associated with an increased risk of developing HBOS (or HBOC syndrome). The KRAS-Variant was found in approximately 22% of BRCA-positive and 61% of BRCA-negative ovarian cancer patients from HBOC families. Interestingly, unlike BRCA mutations that are widely associated with HBOS (or HBOC syndrome) in individuals of Jewish descent, specifically, Ashkenazi descent, the KRAS-Variant does not appear to be primarily associated with individuals of Jewish descent. Thus, the KRAS-Variant provides a powerful tool for identifying HBOS (or HBOC syndrome) in BRCA-negative and non-Jewish individuals. Furthermore, the presence of both the KRAS-Variant and a BRCA1 mutation results in an increased the risk of that patient developing both breast and ovarian cancers. Over 60% of the individuals in the study who had both ovarian and breast cancer had both the KRAS-Variant and a BRCA1 mutation.
Accordingly, the invention features methods of predicting an increased risk of developing hereditary breast/ovarian cancer syndrome (HBOS or HBOC syndrome) in a subject, including detecting a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample. The presence of the SNP indicates an increased risk of HBOS (or HBOC syndrome) in the subject.
In one aspect, the invention provides methods of identifying SNPs which increase the risk, susceptibility, or probability of developing a HBOS (HBOC syndrome). For example, a subject's risk of developing HBOS (HBOC syndrome), is determined by detecting a mutation in the 3′ untranslated region (UTR) of a member of the KRAS gene superfamily. Specifically the mutation that is detected is a SNP at position 4 of LCS6 of KRAS of which results in a uracil (U) or thymine (T) to guanine (G) conversion.
The invention also features methods of predicting an increased risk of developing ovarian cancer or breast cancer in a subject, including detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of the BRCA1 mutation and the SNP indicates an increased risk developing breast or ovarian cancer.
The invention further features methods of predicting an increased risk of developing both breast and ovarian cancer in a subject having HBOS (or HBOC syndrome) including detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of the BRCA1 mutation and the SNP indicates an increased risk developing both breast and ovarian cancer.
Identification of the mutation indicates an increases risk of developing HBOS (or HBOC syndrome). “Risk” in the context of the present invention, relates to the probability that an event will occur over a specific time period, and can mean a subject's “absolute” risk or “relative” risk. Absolute risk can be measured with reference to either actual observation post-measurement for the relevant time cohort, or with reference to index values developed from statistically valid historical cohorts that have been followed for the relevant time period. Relative risk refers to the ratio of absolute risks of a subject compared either to the absolute risks of low risk cohorts or an average population risk, which can vary by how clinical risk factors are assessed. Odds ratios, the proportion of positive events to negative events for a given test result, are also commonly used (odds are according to the formula p/(1−p) where p is the probability of event and (1−p) is the probability of no event) to no-conversion.
“Risk evaluation,” or “evaluation of risk” in the context of the present invention encompasses making a prediction of the probability, odds, or likelihood that an event or disease state may occur, the rate of occurrence of the event or conversion from one disease state to another, i.e., from a primary tumor to a metastatic tumor or to one at risk of developing a metastatic, or from at risk of a primary metastatic event to a secondary metastatic event or from at risk of a developing a primary tumor of one type to developing a one or more primary tumors of a different type. Risk evaluation can also comprise prediction of future clinical parameters, traditional laboratory risk factor values, or other indices of cancer, either in absolute or relative terms in reference to a previously measured population.
An “increased risk” is meant to describe an increased probably that an individual who carries the KRAS-Variant, has HBOS (HBOC syndrome) and develop breast or ovarian cancer, compared to an individual who does not carry KRAS-Variant. In certain embodiments, a KRAS-Variant carrier is 1.5×, 2×, 2.5×, 3×, 3.5×, 4×, 4.5×, 5×, 5.5×, 6×, 6.5×, 7×, 7.5×, 8×, 8.5×, 9×, 9.5×, 10×, 20×, 30×, 40×, 50×, 60×, 70×, 80×, 90×, or 100× more likely to have HBOS (or HBOC syndrome) and develop breast or ovarian cancer than an individual who does not carry the KRAS-Variant.
By poor prognosis is meant that the probability of the individual surviving the development of particularly aggressive or high-risk subtypes of cancer is less than the probability of surviving more benign forms. Poor prognosis is also meant to describe a less satisfactory recovery, longer recovery period, more invasive or high-risk therapeutic regime, or an increased probability of reoccurrence of the cancer. It has been shown that the KRAS-Variant is predicative of the occurrence of aggressive subtypes of cancer. These aggressive subtypes of cancers are associated with the worst prognosis of each of these cancers resulting in a poor prognosis.
A subject is preferably a mammal. The mammal can be a human, non-human primate, mouse, rat, dog, cat, horse, or cow, but are not limited to these examples. A subject can be male or female. A subject is one who has not been previously diagnosed as having HBOS (or HBOC syndrome). The subject can be one who exhibits one or more risk factors for HBOS (or HBOC syndrome). Alternatively, the subject does not exhibit a risk factor for HBOS (or HBOC syndrome). HBOS (or HBOC syndrome) risk factors include for example, a parent or sibling who has been diagnosed with breast cancer, ovarian cancer, or both; a parent or sibling who has been diagnosed with pre-menopausal breast cancer; and Ashkenazi Jewish ancestry. The subject is BRCA-1 and/or BRCA-2 negative. Alternatively, the subject is BRCA-1 and/or BRCA-2 positive. In certain aspects, subjects are carriers of non-founder BRCA1 mutations. The subject is of Jewish descent. For example, the subject is of Ashkenazi Jewish descent. Alternatively, the subject is not of Jewish descent.
The biological sample can be any tissue or fluid that contains nucleic acids. Various embodiments include paraffin imbedded tissue, frozen tissue, surgical fine needle aspirations, and cells of the breast, endometrium, ovaries, uterus, or cervix. Other embodiments include fluid samples such peripheral blood lymphocytes, lymph fluid, ascites, serous fluid, sputum, and stool or urinary specimens such as bladder washing and urine.
Linkage disequilibrium (LD) refers to the co-inheritance of alleles (e.g., alternative nucleotides) at two or more different SNP sites at frequencies greater than would be expected from the separate frequencies of occurrence of each allele in a given population. The expected frequency of co-occurrence of two alleles that are inherited independently is the frequency of the first allele multiplied by the frequency of the second allele. Alleles that co-occur at expected frequencies are said to be in “linkage equilibrium”. In contrast, LD refers to any non-random genetic association between allele(s) at two or more different SNP sites, which is generally due to the physical proximity of the two loci along a chromosome. LD can occur when two or more SNPs sites are in close physical proximity to each other on a given chromosome and therefore alleles at these SNP sites will tend to remain unseparated for multiple generations with the consequence that a particular nucleotide (allele) at one SNP site will show a non-random association with a particular nucleotide (allele) at a different SNP site located nearby. Hence, genotyping one of the SNP sites will give almost the same information as genotyping the other SNP site that is in LD.
For screening individuals for genetic disorders (e.g. prognostic or risk) purposes, if a particular SNP site is found to be useful for screening a disorder, then the skilled artisan would recognize that other SNP sites which are in LD with this SNP site would also be useful for screening the condition. Various degrees of LD can be encountered between two or more SNPs with the result being that some SNPs are more closely associated (i.e., in stronger LD) than others. Furthermore, the physical distance over which LD extends along a chromosome differs between different regions of the genome, and therefore the degree of physical separation between two or more SNP sites necessary for LD to occur can differ between different regions of the genome.
For screening applications, polymorphisms (e.g., SNPs and/or haplotypes) that are not the actual disease-causing (causative) polymorphisms, but are in LD with such causative polymorphisms, are also useful. In such instances, the genotype of the polymorphism(s) that is/are in LD with the causative polymorphism is predictive of the genotype of the causative polymorphism and, consequently, predictive of the phenotype (e.g., disease) that is influenced by the causative SNP(s). Thus, polymorphic markers that are in LD with causative polymorphisms are useful as markers, and are particularly useful when the actual causative polymorphism(s) is/are unknown.
Linkage disequilibrium in the human genome is reviewed in: Wall et al., “Haplotype blocks and linkage disequilibrium in the human genome”, Nat Rev Genet. 2003 August; 4(8):587-97; Gamer et al., “On selecting markers for association studies: patterns of linkage disequilibrium between two and three diallelic loci”, Genet Epidemiol. 2003 January; 24 (1):57-67; Ardlie et al., “Patterns of linkage disequilibrium in the human genome”, Nat Rev Genet. 2002 April; 3 (4):299-309 (erratum in Nat Rev Genet 2002 July; 3 (7):566); and Remm et al., “High-density genotyping and linkage disequilibrium in the human genome using chromosome 22 as a model”; Curr Opin Chem Biol. 2002 February; 6 (1):24-30.
The screening techniques of the present invention may employ a variety of methodologies to determine whether a test subject has a SNP or a SNP pattern associated with an increased or decreased risk of developing a detectable trait or whether the individual suffers from a detectable trait as a result of a particular polymorphism/mutation, including, for example, methods which enable the analysis of individual chromosomes for haplotyping, family studies, single sperm DNA analysis, or somatic hybrids. The trait analyzed using the diagnostics of the invention may be any detectable trait that is commonly observed in pathologies and disorders.
SNP Genotyping MethodsThe process of determining which specific nucleotide (i.e., allele) is present at each of one or more SNP positions, such as a SNP position in a nucleic acid molecule disclosed in SEQ ID NO: 11, 12 or 13, is referred to as SNP genotyping. The present invention provides methods of SNP genotyping, such as for use in screening for a variety of disorders, or determining predisposition thereto, or determining responsiveness to a form of treatment, or prognosis, or in genome mapping or SNP association analysis, etc.
Nucleic acid samples can be genotyped to determine which allele(s) is/are present at any given genetic region (e.g., SNP position) of interest by methods well known in the art. The neighboring sequence can be used to design SNP detection reagents such as oligonucleotide probes, which may optionally be implemented in a kit format. Exemplary SNP genotyping methods are described in Chen et al., “Single nucleotide polymorphism genotyping: biochemistry, protocol, cost and throughput”, Pharmacogenomics J. 2003; 3 (2):77-96; Kwok et al., “Detection of single nucleotide polymorphisms”, Curr Issues Mol. Biol. 2003 April; 5 (2):43-60; Shi, “Technologies for individual genotyping: detection of genetic polymorphisms in drug targets and disease genes”, Am J Pharmacogenomics. 2002; 2 (3):197-205; and Kwok, “Methods for genotyping single nucleotide polymorphisms”, Annu Rev Genomics Hum Genet 2001; 2:235-58. Exemplary techniques for high-throughput SNP genotyping are described in Marnellos, “High-throughput SNP analysis for genetic association studies”, Curr Opin Drug Discov Devel. 2003 May; 6 (3):317-21. Common SNP genotyping methods include, but are not limited to, TaqMan assays, molecular beacon assays, nucleic acid arrays, allele-specific primer extension, allele-specific PCR, arrayed primer extension, homogeneous primer extension assays, primer extension with detection by mass spectrometry, pyrosequencing, multiplex primer extension sorted on genetic arrays, ligation with rolling circle amplification, homogeneous ligation, OLA (U.S. Pat. No. 4,988,167), multiplex ligation reaction sorted on genetic arrays, restriction-fragment length polymorphism, single base extension-tag assays, and the Invader assay. Such methods may be used in combination with detection mechanisms such as, for example, luminescence or chemiluminescence detection, fluorescence detection, time-resolved fluorescence detection, fluorescence resonance energy transfer, fluorescence polarization, mass spectrometry, and electrical detection.
Various methods for detecting polymorphisms include, but are not limited to, methods in which protection from cleavage agents is used to detect mismatched bases in RNA/RNA or RNA/DNA duplexes (Myers et al., Science 230:1242 (1985); Cotton et al., PNAS 85:4397 (1988); and Saleeba et al., Meth. Enzymol. 217:286-295 (1992)), comparison of the electrophoretic mobility of variant and wild type nucleic acid molecules (Orita et al., PNAS 86:2766 (1989); Cotton et al., Mutat. Res. 285:125-144 (1993); and Hayashi et al., Genet. Anal. Tech. Appl. 9:73-79 (1992)), and assaying the movement of polymorphic or wild-type fragments in polyacrylamide gels containing a gradient of denaturant using denaturing gradient gel electrophoresis (DGGE) (Myers et al., Nature 313:495 (1985)). Sequence variations at specific locations can also be assessed by nuclease protection assays such as RNase and SI protection or chemical cleavage methods.
In a preferred embodiment, SNP genotyping is performed using the TaqMan assay, which is also known as the 5′ nuclease assay (U.S. Pat. Nos. 5,210,015 and 5,538,848). The TaqMan assay detects the accumulation of a specific amplified product during PCR. The TaqMan assay utilizes an oligonucleotide probe labeled with a fluorescent reporter dye and a quencher dye. The reporter dye is excited by irradiation at an appropriate wavelength, it transfers energy to the quencher dye in the same probe via a process called fluorescence resonance energy transfer (FRET). When attached to the probe, the excited reporter dye does not emit a signal. The proximity of the quencher dye to the reporter dye in the intact probe maintains a reduced fluorescence for the reporter. The reporter dye and quencher dye may be at the 5′ most and the 3′ most ends, respectively, or vice versa. Alternatively, the reporter dye may be at the 5′ or 3′ most end while the quencher dye is attached to an internal nucleotide, or vice versa. In yet another embodiment, both the reporter and the quencher may be attached to internal nucleotides at a distance from each other such that fluorescence of the reporter is reduced.
During PCR, the 5′ nuclease activity of DNA polymerase cleaves the probe, thereby separating the reporter dye and the quencher dye and resulting in increased fluorescence of the reporter. Accumulation of PCR product is detected directly by monitoring the increase in fluorescence of the reporter dye. The DNA polymerase cleaves the probe between the reporter dye and the quencher dye only if the probe hybridizes to the target SNP-containing template which is amplified during PCR, and the probe is designed to hybridize to the target SNP site only if a particular SNP allele is present.
Preferred TaqMan primer and probe sequences can readily be determined using the SNP and associated nucleic acid sequence information provided herein. A number of computer programs, such as Primer Express (Applied Biosystems, Foster City, Calif.), can be used to rapidly obtain optimal primer/probe sets. It will be apparent to one of skill in the art that such primers and probes for detecting the SNPs of the present invention are useful in prognostic assays for a variety of disorders including cancer, and can be readily incorporated into a kit format. The present invention also includes modifications of the Taqman assay well known in the art such as the use of Molecular Beacon probes (U.S. Pat. Nos. 5,118,801 and 5,312,728) and other variant formats (U.S. Pat. Nos. 5,866,336 and 6,117,635).
The identity of polymorphisms may also be determined using a mismatch detection technique, including but not limited to the RNase protection method using riboprobes (Winter et al., Proc. Natl. Acad Sci. USA 82:7575, 1985; Meyers et al., Science 230:1242, 1985) and proteins which recognize nucleotide mismatches, such as the E. coli mutS protein (Modrich, P. Ann. Rev. Genet. 25:229-253, 1991). Alternatively, variant alleles can be identified by single strand conformation polymorphism (SSCP) analysis (Orita et al., Genomics 5:874-879, 1989; Humphries et al., in Molecular Diagnosis of Genetic Diseases, R. Elles, ed., pp. 321-340, 1996) or denaturing gradient gel electrophoresis (DGGE) (Wartell et al., Nuci. Acids Res. 18:2699-2706, 1990; Sheffield et al., Proc. Natl. Acad. Sci. USA 86:232-236, 1989).
A polymerase-mediated primer extension method may also be used to identify the polymorphism(s). Several such methods have been described in the patent and scientific literature and include the “Genetic Bit Analysis” method (WO92/15712) and the ligase/polymerase mediated genetic bit analysis (U.S. Pat. No. 5,679,524). Related methods are disclosed in WO91/02087, WO90/09455, WO95/17676, U.S. Pat. Nos. 5,302,509, and 5,945,283. Extended primers containing a polymorphism may be detected by mass spectrometry as described in U.S. Pat. No. 5,605,798. Another primer extension method is allele-specific PCR (Ruano et al., Nucl. Acids Res. 17:8392, 1989; Ruano et al., Nucl. Acids Res. 19, 6877-6882, 1991; WO 93/22456; Turki et al., J Clin. Invest. 95:1635-1641, 1995). In addition, multiple polymorphic sites may be investigated by simultaneously amplifying multiple regions of the nucleic acid using sets of allele-specific primers as described in Wallace et al. (WO89/10414).
Another preferred method for genotyping the SNPs of the present invention is the use of two oligonucleotide probes in an OLA (see, e.g., U.S. Pat. No. 4,988,617). In this method, one probe hybridizes to a segment of a target nucleic acid with its 3′ most end aligned with the SNP site. A second probe hybridizes to an adjacent segment of the target nucleic acid molecule directly 3′ to the first probe. The two juxtaposed probes hybridize to the target nucleic acid molecule, and are ligated in the presence of a linking agent such as a ligase if there is perfect complementarity between the 3′ most nucleotide of the first probe with the SNP site. If there is a mismatch, ligation would not occur. After the reaction, the ligated probes are separated from the target nucleic acid molecule, and detected as indicators of the presence of a SNP.
The following patents, patent applications, and published international patent applications, which are all hereby incorporated by reference, provide additional information pertaining to techniques for carrying out various types of OLA: U.S. Pat. Nos. 6,027,889, 6,268,148, 5,494,810, 5,830,711, and 6054564 describe OLA strategies for performing SNP detection; WO 97/31256 and WO 00/56927 describe OLA strategies for performing SNP detection using universal arrays, wherein a zipcode sequence can be introduced into one of the hybridization probes, and the resulting product, or amplified product, hybridized to a universal zip code array; U.S. application US01/17329 (and Ser. No. 09/584,905) describes OLA (or LDR) followed by PCR, wherein zipcodes are incorporated into OLA probes, and amplified PCR products are determined by electrophoretic or universal zipcode array readout; U.S. application 60/427,818, 60/445,636, and 60/445,494 describe SNPlex methods and software for multiplexed SNP detection using OLA followed by PCR, wherein zipcodes are incorporated into OLA probes, and amplified PCR products are hybridized with a zipchute reagent, and the identity of the SNP determined from electrophoretic readout of the zipchute. In some embodiments, OLA is carried out prior to PCR (or another method of nucleic acid amplification). In other embodiments, PCR (or another method of nucleic acid amplification) is carried out prior to OLA.
Another method for SNP genotyping is based on mass spectrometry. Mass spectrometry takes advantage of the unique mass of each of the four nucleotides of DNA. SNPs can be unambiguously genotyped by mass spectrometry by measuring the differences in the mass of nucleic acids having alternative SNP alleles. MALDI-TOF (Matrix Assisted Laser Desorption Ionization—Time of Flight) mass spectrometry technology is preferred for extremely precise determinations of molecular mass, such as SNPs. Numerous approaches to SNP analysis have been developed based on mass spectrometry. Preferred mass spectrometry-based methods of SNP genotyping include primer extension assays, which can also be utilized in combination with other approaches, such as traditional gel-based formats and microarrays.
Typically, the primer extension assay involves designing and annealing a primer to a template PCR amplicon upstream (5′) from a target SNP position. A mix of dideoxynucleotide triphosphates (ddNTPs) and/or deoxynucleotide triphosphates (dNTPs) are added to a reaction mixture containing template (e.g., a SNP-containing nucleic acid molecule which has typically been amplified, such as by PCR), primer, and DNA polymerase. Extension of the primer terminates at the first position in the template where a nucleotide complementary to one of the ddNTPs in the mix occurs. The primer can be either immediately adjacent (i.e., the nucleotide at the 3′ end of the primer hybridizes to the nucleotide next to the target SNP site) or two or more nucleotides removed from the SNP position. If the primer is several nucleotides removed from the target SNP position, the only limitation is that the template sequence between the 3′ end of the primer and the SNP position cannot contain a nucleotide of the same type as the one to be detected, or this will cause premature termination of the extension primer. Alternatively, if all four ddNTPs alone, with no dNTPs, are added to the reaction mixture, the primer will always be extended by only one nucleotide, corresponding to the target SNP position. In this instance, primers are designed to bind one nucleotide upstream from the SNP position (i.e., the nucleotide at the 3′ end of the primer hybridizes to the nucleotide that is immediately adjacent to the target SNP site on the 5′ side of the target SNP site). Extension by only one nucleotide is preferable, as it minimizes the overall mass of the extended primer, thereby increasing the resolution of mass differences between alternative SNP nucleotides. Furthermore, mass-tagged ddNTPs can be employed in the primer extension reactions in place of unmodified ddNTPs. This increases the mass difference between primers extended with these ddNTPs, thereby providing increased sensitivity and accuracy, and is particularly useful for typing heterozygous base positions. Mass-tagging also alleviates the need for intensive sample-preparation procedures and decreases the necessary resolving power of the mass spectrometer.
The extended primers can then be purified and analyzed by MALDI-TOF mass spectrometry to determine the identity of the nucleotide present at the target SNP position. In one method of analysis, the products from the primer extension reaction are combined with light absorbing crystals that form a matrix. The matrix is then hit with an energy source such as a laser to ionize and desorb the nucleic acid molecules into the gas-phase. The ionized molecules are then ejected into a flight tube and accelerated down the tube towards a detector. The time between the ionization event, such as a laser pulse, and collision of the molecule with the detector is the time of flight of that molecule. The time of flight is precisely correlated with the mass-to-charge ratio (m/z) of the ionized molecule. Ions with smaller m/z travel down the tube faster than ions with larger m/z and therefore the lighter ions reach the detector before the heavier ions. The time-of-flight is then converted into a corresponding, and highly precise, m/z. In this manner, SNPs can be identified based on the slight differences in mass, and the corresponding time of flight differences, inherent in nucleic acid molecules having different nucleotides at a single base position. For further information regarding the use of primer extension assays in conjunction with MALDI-TOF mass spectrometry for SNP genotyping, see, e.g., Wise et al., “A standard protocol for single nucleotide primer extension in the human genome using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry”, Rapid Commun Mass Spectrom. 2003; 17 (11):1195-202.
The following references provide further information describing mass spectrometry-based methods for SNP genotyping: Bocker, “SNP and mutation discovery using base-specific cleavage and MALDI-TOF mass spectrometry”, Bioinformatics. 2003 July; 19 Suppl 1:144-153; Storm et al., “MALDI-TOF mass spectrometry-based SNP genotyping”, Methods Mol. Biol. 2003; 212:241-62; Jurinke et al., “The use of MassARRAY technology for high throughput genotyping”, Adv Biochem Eng Biotechnol. 2002; 77:57-74; and Jurinke et al., “Automated genotyping using the DNA MassArray technology”, Methods Mol. Biol. 2002; 187:179-92.
SNPs can also be scored by direct DNA sequencing. A variety of automated sequencing procedures can be utilized ((1995) Biotechniques 19:448), including sequencing by mass spectrometry (see, e.g., PCT International Publication No. WO94/16101; Cohen et al., Adv. Chromatogr. 36:127-162 (1996); and Griffin et al., Appl. Biochem. Biotechnol. 38:147-159 (1993)). The nucleic acid sequences of the present invention enable one of ordinary skill in the art to readily design sequencing primers for such automated sequencing procedures. Commercial instrumentation, such as the Applied Biosystems 377, 3100, 3700, 3730, and 3730.times.1 DNA Analyzers (Foster City, Calif.), is commonly used in the art for automated sequencing.
Other methods that can be used to genotype the SNPs of the present invention include single-strand conformational polymorphism (SSCP), and denaturing gradient gel electrophoresis (DGGE) (Myers et al., Nature 313:495 (1985)). SSCP identifies base differences by alteration in electrophoretic migration of single stranded PCR products, as described in Orita et al., Proc. Nat. Acad. Single-stranded PCR products can be generated by heating or otherwise denaturing double stranded PCR products. Single-stranded nucleic acids may refold or form secondary structures that are partially dependent on the base sequence. The different electrophoretic mobilities of single-stranded amplification products are related to base-sequence differences at SNP positions. DGGE differentiates SNP alleles based on the different sequence-dependent stabilities and melting properties inherent in polymorphic DNA and the corresponding differences in electrophoretic migration patterns in a denaturing gradient gel (Erlich, ed., PCR Technology, Principles and Applications for DNA Amplification, W. H. Freeman and Co, New York, 1992, Chapter 7).
Sequence-specific ribozymes (U.S. Pat. No. 5,498,531) can also be used to score SNPs based on the development or loss of a ribozyme cleavage site. Perfectly matched sequences can be distinguished from mismatched sequences by nuclease cleavage digestion assays or by differences in melting temperature. If the SNP affects a restriction enzyme cleavage site, the SNP can be identified by alterations in restriction enzyme digestion patterns, and the corresponding changes in nucleic acid fragment lengths determined by gel electrophoresis
SNP genotyping can include the steps of, for example, collecting a biological sample from a human subject (e.g., sample of tissues, cells, fluids, secretions, etc.), isolating nucleic acids (e.g., genomic DNA, mRNA or both) from the cells of the sample, contacting the nucleic acids with one or more primers which specifically hybridize to a region of the isolated nucleic acid containing a target SNP under conditions such that hybridization and amplification of the target nucleic acid region occurs, and determining the nucleotide present at the SNP position of interest, or, in some assays, detecting the presence or absence of an amplification product (assays can be designed so that hybridization and/or amplification will only occur if a particular SNP allele is present or absent). In some assays, the size of the amplification product is detected and compared to the length of a control sample; for example, deletions and insertions can be detected by a change in size of the amplified product compared to a normal genotype.
EXAMPLES Example 1 Prevalence of the KRAS-VariantAs shown in
The KRAS-Variant, is present in up to 27% of newly diagnosed ovarian cancer patients. Among patients of Northern Italian origin (providing 215 samples to the study), the KRAS-Variant was present in 25% of the samples provided. Thus, the positive predictive value within this population is 6%, which means that 1 of every 16 KRAS-Variant-positive individual will develop ovarian cancer.
Among patients treated at Yale University, the prevalence of the KRAS-Variant was approximately the same as in the Northern Italian patient group. Yale University patients provided 100 samples to the study. The KRAS-Variant was found in 36% of those samples. Thus, the positive predictive value within the Yale University patient population is also 6%. Similar to the Northern Italian population, these results show that 1 of every 16 KRAS-Variant-positive individuals will develop ovarian cancer.
About 1/4 of all ovarian cancer patients have the KRAS-Variant (
Comparisons of “wild-type” individuals and those individuals carrying the KRAS-Variant revealed that the presence of the KRAS-Variant is predictive of a 2.0-fold increased risk of developing ovarian cancer compared to those who do not carry either a single or double copy of the mutation. Comparisons were adjusted for both age and race.
When age is considered, comparisons between wild type or normal individuals who do not carry the KRAS-Variant and those individuals who carry either a one or two copies of the KRAS-Variant reveal that the KRAS-Variant (or Onco-SNP) is as prevalent in older women as younger women (Table 2). Moreover, the prevalence of the KRAS-Variant in women of various ages does not vary by ovarian cancer subtype. The KRAS-Variant is not associated with cancer for younger women.
In a comparison of KRAS-Variant and non-KRAS-Variant ovarian cancer patients, it was determined that the median age of ovarian cancer onset for someone with the KRAS-Variant was younger than someone who did not have the KRAS-Variant (referred to as a non-KRAS-Variant patient). KRAS-Variant carriers presented ovarian cancer onset at an average age of 57.8 years versus 59 years of age for non-SNP patients (
Moreover, results of ovarian subtype comparisons revealed significant differences in progression-free survival (PFS) or overall survival (OS). Table 3 shows an ovarian cancer subtype analysis quantifying the number (and percentage) of patients having each cancer type, broken down by KRAS-Variant status. The data show that the association of KRAS-Variant with non-mucinous ovarian cancer is significantly higher than in mucinous cancer (p=0.031 which is less that 0.05).
A corroborating study also demonstrated that the KRAS-Variant, or Onco-SNP is rare in ovarian cancer patients with mucinous tumors (Table 4).
Ovarian cancer patients provided four-generation pedigrees that included occurrences of both breast and ovarian cancer. Furthermore, the BRCA1 and BRCA2 status of each ovarian cancer patient included in the study was known. Among these study participants, 36 BRCA-positive ovarian cancer patients were assessed for the presence of the KRAS-Variant. Among these BRCA-positive individuals, 30% (or 23 individuals) were positive for both the BRCA1 and the KRAS-Variant mutations. Moreover, 8% (or 13 individuals) were positive for both the BRCA2 and the KRAS-Variant mutations. These same results were demonstrated when breast cancer patients were evaluated. Also, in this study, 31 BRCA-negative ovarian cancer patients were assessed for the presence of the KRAS-Variant. Among this BRCA-negative ovarian cancer population, 61% of the individuals were positive for the KRAS-Variant with a statistical significance of p<0.0001. As a result of this study, the positive predictive value (PPV) of the KRAS-Variant mutation increased to 7.4%. Thus, 1 of 12 people with the KRAS-Variant is at risk of developing ovarian cancer consistent with a family history of HBOC syndrome (or HBOS). The negative predictive value (NPV) of the KRAS-Variant mutation was 99.4% (1/167 risk). Individuals who carry the KRAS-Variant are 6× more likely to develop ovarian cancer.
The data show that the presence or absence of the KRAS-Variant is a more reliable predictor of the risk of developing hereditary breast/ovarian cancer (HBOC) than BRCA. BRCA is only effective as a predictive marker, rather than a risk factor, for about 5% of patients, who are usually of Ashkenazi, Eastern European, Jewish backgrounds. Genetic tests for the presence of KRAS-Variant, either alone, or in combination with BRCA, are used to predict the risk of breast and/or ovarian cancer in any patient. The KRAS-Variant test is particularly valuable for those patients who are BRCA-negative, and for whom, until now, no test has existed. The KRAS-Variant test is not only a valuable initial screening tool, because of the simplicity of the test, compared to BRCA for instance, but the KRAS-Variant test is of particular value for BRCA-negative and HBOS (or HBOC syndrome) individuals. An HBOS (or HBOC syndrome) individual is someone who has either themselves been diagnosed with Hereditary Breast/Ovarian Syndrome (HBOS or HBOC syndrome), or is related to someone diagnosed with HBOS (or HBOC syndrome).
Importantly, the data show that while BRCA and KRAS-Variant are individually predictive of cancer risk, the occurrence of both mutations in the same individual has an additive, and probably a synergistic effect. For instance, of the co-positive patients in this study, approximately 65% had both ovarian and breast cancer. Individually, the KRAS-Variant occurs in one third of ovarian cancer cases. The BRCA1 mutation occurred in 34% of the ovarian cancer patients of this study. Of the 30% of ovarian cancer patient who were co-positive for BRCA1 and KRAS-Variant, a resounding 65% had developed both cancers.
BRCA-positive patients represent a small proportion of the population, approximately less than 10 percent of ovarian cancer patients. In contrast, the KRAS-Variant occurs in 36 percent of ovarian cancer patients.
Similar results were demonstrated in breast cancer BRCA-positive cohort of patients. 29% of 129 BRCA1 positive breast cancer patients were co-positive for the KRAS-variant, whereas 11% of 156 BRCA2 positive breast cancer patients were co-positive for the KRAS-variant
Example 6 Association of the KRAS-Variant with Hereditary Breast/Ovarian CancerThe relative prevalence of the BRCA1, BRCA2, and KRAS-Variant mutations were assessed within various ethnic, diagnostic, and age groups.
The data of
Comparisons of individuals who do not carry the KRAS-Variant (or the Onco SNP), labeled as “00”, and those individuals who carry one or two copies of the KRAS-Variant, “1/2,” revealed that the presence of the KRAS-Variant is associated with more advanced cancer, which is classified as stage III-IV (Table 5). Moreover, the KRAS-Variant is also associated with more aggressive ovarian cancer, which is non-responsive or less responsive to known treatments (Table 5).
Comparisons of individuals who do not carry the KRAS-Variant, labeled as “00”, and those individuals who carry one or two copies of the KRAS-Variant, “Variant (heter/homoz),” revealed that the presence of the KRAS-Variant is associated with more poor prognosis, which is reflects poor survival or increased rates of patient death (Table 6). The multivariate comparisons were adjusted for age and ethnicity.
The KRAS-Variant is associated with ovarian cancer risk for sporadic ovarian cancer. To further validate the role of the KRAS-Variant as a genetic marker of ovarian cancer, those ovarian cancer patients who were considered to be at high-risk for having a familial genetic abnormality with a family history consistent with Hereditary Breast and Ovarian Cancer (HBOC) Syndrome were further examined for the presence of the KRAS-Variant. These patients had either a personal and/or family history (within 1st or 2nd degree relatives) of at least one additional case of ovarian cancer and/or breast cancer. Moreover, all of the patients included in this study were of European ancestry. All of the study participants had also undergone BRCA mutation analysis. Sixty-seven patients fit the following parameters: 23 were positive for BRCA1 mutations; 13 were positive for BRCA2 mutations; and 31 were uninformative (negative for both BRCA1 and BRCA2 mutations). Overall, 8/36 (or 22%) of BRCA mutation carriers were carriers for the KRAS-Variant. Specifically, 7/23 (or 30%) of BRCA1 mutant carriers were co-positive for the KRAS-Variant and 1/13 (or 8%) of BRCA2 mutant carriers were co-positive for the KRAS-Variant. The differential association of the KRAS-Variant with BRCA1 and BRCA2 represents a biological modification of BRCA penetrance by the KRAS-Variant.
Enhancement of BRCA1 by the KRAS-Variant was tested in a larger cohort of breast cancer patients. Of the 300 breast cancer patients that were BRCA1 and BRCA2 positive, 150 had BRCA1 mutations, and 150 had BRCA2 mutations. Similar to the ovarian cancer study, the KRAS-Variant was present in 30% breast cancer patients with the BRCA1 mutation, and in only 10% of breast cancer patients with the BRCA2 mutation. These results confirm our hypothesis that there is an enhanced risk of developing either breast or ovarian cancer for individuals who carry both BRCA1 and the KRAS-Variant.
Segregation analysis is ongoing. The results are expected to reveal an increased risk of developing breast and/or ovarian cancer for individuals who carry the BRCA1 and the KRAS-Variant mutations. The data have demonstrated that an individual is significantly more likely to develop breast or ovarian cancer when she carries a BRCA1 mutation and the KRAS-Variant. Thus, the KRAS-Variant modifies BRCA1 penetrance. In fact, the KRAS-Variant is one of the strongest known modifiers of BRCA1 penetrance.
Example 10 The KRAS-Variant is a Genetic Marker of Ovarian Cancer RiskOvarian cancer is the single most deadly form of womens cancer, largely due to patients presenting with advanced disease due to a lack of known risk factors or genetic markers of risk. The KRAS oncogene and altered levels of the microRNA let-7 are associated with an increased risk of developing solid tumors. The association of the variant (derived) allele at rs61764370, referred to as the KRAS-Variant, previously shown to disrupt a let-7 microRNA binding site in the KRAS oncogene, was investigated and demonstrated increased ovarian cancer risk.
Specimens were obtained and tested for the presence of the KRAS-Variant from non-selected ovarian cancer patients in three independent cohorts (n=472), from two independent ovarian casecontrol studies (n=866), and from ovarian cancer patients with hereditary breast and ovarian cancer (HBOC) syndrome (n=67) as well as in their family members.
The results indicate that the KRAS-variant is associated with greater than 25% of non-selected ovarian cancer cases, and is a marker for a significant increased risk of developing ovarian cancer as confirmed by two independent case control analyses. In addition, the KRAS-variant was identified in 61% of HBOC patients without BRCA1 or BRCA2 mutations, previously considered uninformative, as well as in their family members with cancer. These findings strongly suggest that the KRAS-variant is a genetic marker of an increased risk of developing ovarian cancer, and further suggests that the KRAS-variant is a new genetic marker of cancer risk for HBOC families without other known genetic abnormalities.
The KRAS-Variant and Ovarian Cancer RiskWomen with epithelial ovarian cancer (OC) who presented at Yale/New Haven Hospital for surgery (n=157) were tested for the KRAS-variant. It was discovered that over 27% of these women harbored this variant-allele. Because this was a significantly higher prevalence than previously shown in any normal or cancerous population (18%, 14, 22 and >9,000 additional people tested), this finding was validated in two additional, independent cohorts of epithelial OC patients. The first was from the University Hospital in Northern Italy at the University of Turin (n=215), and 26% of patients harbored the KRAS-variant in this cohort. The second was from Brescia, Italy (n=100), and again 25% of these OC patients carried the KRAS-variant. The frequency of the KRAS-variant was thus significantly higher in these OC cohorts than in any group previously studied, including non-cancerous controls collected at Yale New Haven Hospital (
To investigate if the KRAS-variant predicts an increased risk of developing OC for non-selected female populations, case-control analyses were performed. The Yale Case-Control contained 100 cases and 101 controls and showed a significantly increased risk of developing OC for KRAS-variant carriers by multivariate analysis (OR=2.46, CI=1.14-5.29, p=0.020). These findings were validated in a second independent case control: the Connecticut Ovarian Cancer Case-Control consists of 320 patients and 328 controls, and also showed a significant increased risk of developing OC for the KRAS-variant carriers by multivariate analysis (OR=1.7, CI=1.11-2.63, p=0.016) (Table 1). These findings suggest that the KRAS-variant is a genetic marker of an increased risk of developing OC in non-selected women.
Ovarian Cancer Variables and the KRAS-VariantThe distribution of the KRAS-variant was evaluated in the different subtypes of epithelial OC. It was found that the prevalence of the KRAS-variant varied between subtypes, being most common in non-mucinous cancers, but was rarely found in patients with mucinous ovarian cancers (p<0.05, Table 4).
A range of variables were studied to determine if there were specific characteristics segregating OC patients harboring the KRAS-variant versus those without. It was found that in patients with available data there was not a significant difference in patient age at first surgery, tumor grade, residual tumor size, debulking, stage of OC presentation, response to platinum-based chemotherapy, or progression free survival (hazard ratio (HR)=1.12, 95% CI 0.71-1.76) (Table 7).
The trend towards worse progression free survival for OC patients harboring the KRAS-variant suggests an impact of the KRAS-variant on ovarian cancer outcome. Because the KRAS-variant is located in the 3′UTR of the KRAS oncogene, available tumor samples were tested for KRAS codon mutations (n=6 KRAS-variant harboring patients, n=10 KRAS-variant non-harboring patients). Not surprisingly, as non-mucinous OC rarely has activated KRAS, none of the ovarian tumors tested had the common KRAS activating mutations. These findings agree with our prior findings that the KRAS-variant is not enriched in tumors with other tumor-acquired KRAS mutations.
Association of the KRAS-Variant with HBOC Syndrome
As the KRAS-variant appeared to be associated with OC risk for sporadic OC, to further validate its role as a genetic marker of ovarian cancer, OC patients considered to be at high-risk for having a familial genetic abnormality with a family history consistent with HBOC were examined. These patients had either personal and/or family histories (1st or 2nd degree relatives) of at least one additional case of OC and/or breast cancer, and all had undergone BRCA mutation analysis. 67 patients fit these parameters: 23 were positive for BRCA1 mutations; 13 were positive for BRCA2 mutations; and 31 were uninformative (BRCA1 and -2 mutation negative). Overall 8/36 (22%) of BRCA mutation carriers had the KRAS-variant: 7/23 (30%) of BRCA1 mutant carriers and 1/13 (8%) of BRCA2 mutant carriers. The differential association of the KRAS-variant with BRCA1 and BRCA2 may represent a biological modification of BRCA penetrance by the KRAS-variant, a hypothesis that requires additional study.
Of the 31 uninformative HBOC patients with OC, 19/31, or 61% harbored the KRAS-variant, a prevalence significantly higher than documented rates for either the healthy population 14 or other OC patients (p<0.0001 compared to control patients). For a KRAS-variant harboring uninformative HBOC family member this results in a positive predictive value (PPV) for developing OC of 6.78% (95% CI=5.78 to 7.76). In contrast, the negative predictive value (NPV) for a negative KRAS-variant test in an uninformative HBOC family member is 99.37% (95% CI=99.22 to 99.53).
KRAS-Variant Harboring FamiliesAt least two additional family members with known cancer status were tested in four of the uninformative HBOC families whose proband harbored the KRAS-variant and was BRCA negative. In each of these families, at least two relatives diagnosed with cancer also harbored the KRAS-variant (
These results reveal that the variant allele at a polymorphism in the KRAS 3′ UTR, the KRAS-variant, is associated with the risk of developing epithelial OC(OR=2.46), is identified in over 25% of non-selected OC patients and is found in 61% of OC patients from HBOC families previously considered uninformative for gene mutations. These findings support the hypothesis that the KRAS-variant is a new genetic marker of an increased risk of developing OC, and, additionally, suggest that this allele of KRAS may be a new HBOC locus.
While it may seem surprising that a single nucleotide variant could have such predictive power for disease risk, the KRAS-variant represents an entirely different entity than tagging SNPs studied and employed in genome wide association studies. The KRAS-variant is not present on Illumina SNP arrays (being recently discovered and failing design), but rather was identified through a candidate-gene search. It is functional and disrupts a let-7 miRNA binding site that regulates the important human oncogene, KRAS. Perhaps most importantly, the KRAS-variant is an uncommon allele, being in less than 7% of chromosomes in any ethnic group, and would therefore not be meaningfully detected in GWAS studies through LD with more common alleles.
The OC in KRAS-variant carriers has a similar phenotype to the majority of epithelial OC, and occurs primarily in post-menopausal women. This is unlike OC associated with previously identified inherited genetic markers of OC risk, such as BRCA mutations, which disrupt DNA repair pathway genes, and are associated with early onset cancer. This suggests that the KRAS-variant may not act through altered DNA repair, but perhaps instead creates an environment where alterations that occur normally with aging allow aberrant cell growth and oncogenesis. In support of this hypothesis, we previously reported that the KRAS-variant is associated with increased KRAS levels in the background of lower let-7 levels, and others have shown that let-7 levels decrease with age. While KRAS mutations have not been associated with non-mucinous epithelial OC, the KRAS-variant may represent a novel form of KRAS activation, or lead to disruption of the EGFR-signaling pathway, a pathway frequently misregulated in OC. These hypotheses require further validation in OC tumor tissues, a resource that was not available in these studies.
The frequent association of the KRAS-variant with these patients and their family members with cancer suggests that the KRAS-variant is a genetic marker of ovarian cancer risk. Identification of new such markers of ovarian cancer risk is critical for these uninformative families, as those who test positive in these families will have a confirmed increased inherited risk, while those who test negative will in fact be at a decreased risk of developing ovarian cancer compared to the general female population, information that will be equally valuable in their management.
Genetic risk factors for cancer have been historically very difficult to identify, and those that are known are found in very few patients and make up a small minority of cancer cases. Because the 3′ UTR of a gene is a critical regulatory region likely to be bound by multiple miRNAs, we have proposed that this region is likely to harbor variants, such as the KRAS-variant, that may be associated with a large proportion of cancer cases, and be as powerful as gene coding mutations in shaping disease risk.
MethodsSamples from New Haven, Conn., USA
Samples from patients with OC at Yale/New Haven Hospital were recruited and collected from fresh frozen tissue (n=12), paraffin embedded formalin fixed tissue (n=23), blood (n=71) or saliva (n=51) between 2007 and 2009 (total n=157). Since we have previously extensively validated that the KRAS-variant is not somatic but germline (identical in patients' normal and tumor tissues), primarily germline DNA was collected in these studies from either blood or saliva. Patient data was collected including age, ethnicity and family history of cancer.
OC subtype was established by pathologic classification, with only epithelial OC cases included in this study.
OC patients from HBOC families were recruited through the Yale Cancer Center Department of Genetics, and one individual was included from each family as the index case for statistical analysis.
Controls (all female) were recruited from Yale/New Haven Hospital beginning in 2008 from healthy friends and associates of patients, none were genetically related to the patient. All control DNA samples were derived from saliva. None of the controls had any prior diagnosis of cancer (other than nonmelanoma skin cancer).
Information regarding age, ethnicity and family history was recorded.
Samples from Turin, Italy
Between October 1991 and February 2000, there were 264 patients who underwent surgery for ovarian tumors at the department of Gynecology, Gynecologic Oncology Unit, at the University of Turin in Italy, and tissue was collected after institutional IRB approval. All patients were Caucasian. Of these patients, 23 were diagnosed with metastatic cancer, 19 with benign tumors, 6 with OC of nonepithelial origin, and 1 with endometriosis. Epithelial ovarian tumors from the remaining 215 patients were included in this study. Additional details on these samples are available.
Samples from Brescia, Italy
Tumor samples for DNA extraction were collected from 100 patients with epithelial OC at the Division of Gynecologic Oncology at University of Brescia, Italy, between September 2001 and December 2008 after institutional IRB approval. All patients were Caucasian. Clinical data were collected from medical records and were available for all patients. Fifty-nine patients were followed from the date of first surgery until death or May 5, 2009. Patients who received neoadjuvant chemotherapy were excluded from non-static parameters such as debulking, residual disease and PFS.
Case Control AnalysisThe Yale Cases and Controls were selected from those with complete information from Yale/New Haven Hospital (n=100 and 101 respectively). All were women, and were matched for age and ethnicity. For controls who had their ovaries removed for benign reasons, their age at ovarian removal was recorded as their age of testing for this study.
The Connecticut Case-Control study was approved by the Connecticut Department of Public Health and all 32 hospitals that participated. Potential cases were English-speaking women from Connecticut, diagnosed at 35-79 years of age with OC between Sep. 1, 1998 and Feb. 28, 2003, with new primary invasive epithelial ovarian tumors. Controls were a representative sample of the general population of the study area and identified by list-based random digit dialing methods. Cases and controls were matched for age and ethnicity. Cases and controls with prior cancer were excluded from the analysis. Further details are available. Samples used in this study included 320 cases and 328 controls.
Statistical MethodsFor numerical variables (such as age), linear models were used to compare the differences between case and control groups. Chi-square and exact methods were performed to determine the distribution of ethnicity in cases and controls. Hardy-Weinberg testing was analyzed using the ALLELE procedure. Survival analyses were performed using Cox proportional hazards regression model. The association of the KRAS-variant with OC was determined using logistic regression modeling. All statistical analyses were performed using SAS version 9.1.2 (SAS Institute, Cary, N.C.).
Detecting the Presence of the KRAS-VariantDNA was collected using standard isolation methods from tissue, blood, buccal cell samples or saliva. Only the Connecticut Case Control underwent DNA amplification prior to testing. The KRAS-variant was assayed using a allele specific primer and a PCR based Taqman assay using standard techniques. Validation of this assay through duplicate testing and sequencing was previously performed and reported. The KRAS-variant is almost always in the heterozygous state in its carriers, with less then 3-5% of any population containing the variant in the homozygous form. The two genotypes that were combined in this work together as positive for the KRAS-variant.
Calculating Positive Predictive Value (PPV)The PPV is calculated by comparing the percent of KRAS-variant positive and negative patients with ovarian cancer and without and multiplying by a lifetime risk of 1.4% of developing ovarian cancer, to determine the difference in lifetime cancer risk. Control prevalence is based on the Yale controls. PPV is then the lifetime cancer risk of KRAS-variant positive patients with ovarian cancer over the total KRAS-variant people.
While the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.
The patent and scientific literature referred to herein establishes the knowledge that is available to those with skill in the art. All United States patents and published or unpublished United States patent applications cited herein are incorporated by reference. All published foreign patents and patent applications cited herein are hereby incorporated by reference. Genbank and NCBI submissions indicated by accession number cited herein are hereby incorporated by reference. All other published references, documents, manuscripts and scientific literature cited herein are hereby incorporated by reference.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
Claims
1. A method of predicting an increased risk of hereditary breast/ovarian cancer syndrome (HBOC syndrome) in a subject, comprising detecting a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of said SNP indicates an increased risk of HBOC syndrome in said subject.
2. The method of claim 1, wherein said subject is BRCA1 or BRCA2 negative.
3. The method of claim 1, wherein said subject is BRCA1 or BRCA2 positive.
4. The method of claim 1, wherein said subject is of non-Jewish descent.
5. The method of claim 4, wherein said subject is of non-Ashkenazi Jewish descent.
6. A method of predicting an increased risk of developing ovarian cancer or breast cancer in a subject, comprising detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of said BRCA1 mutation and said SNP indicates an increased risk of developing breast or ovarian cancer.
7. The method of claim 6, wherein said subject has HBOS.
8. The method of claim 6, wherein said subject is of non-Jewish descent.
9. The method of claim 8, wherein said subject is of non-Ashkenazi Jewish descent.
10. The method of claim 6, wherein said BRCA1 mutation is a non-founder mutation.
11. The method of claim 6, wherein said subject is BRCA2 negative.
12. A method of predicting an increased risk of developing both breast and ovarian cancer in a subject having HBOCS comprising detecting a BRCA1 mutation and a single nucleotide polymorphism (SNP) at position 4 of the let-7 complementary site 6 of KRAS in a patient sample wherein the presence of said BRCA1 mutation and said SNP indicates an increased risk of developing both breast and ovarian cancer.
13. The method of claim 12, wherein said subject is of non-Jewish descent.
14. The method of claim 13, wherein said subject is of non-Ashkenazi Jewish descent.
15. The method of claim 12, wherein said BRCA1 mutation is a non-founder mutation.
Type: Application
Filed: Feb 5, 2010
Publication Date: Feb 2, 2012
Inventor: Joanne B. Weidhaas (Westport, CT)
Application Number: 13/147,868
International Classification: C12Q 1/68 (20060101);
